1. Field of the Invention
The present invention is generally related to magnetic sensor elements and, more particularly, to a magnetic sensor element made by forming layers of tantalum nitride with a layer of nickel iron, or permalloy, disposed between the layers of tantalum nitride.
2. Description of the Prior Art
In many applications of magnetic sensors, magnetoresistive elements such as nickel iron are used to detect the component of a magnetic field that lies in the plane of the magnetoresistive material. In some applications, the magnetoresistive material is disposed in a serpentine array on a surface of a substrate such as silicon. The serpentine pattern of magnetoresistive material can be connected electrically in a Wheatstone bridge arrangement in order to sense changes in the resistance of the magnetoresistive material in response to changes in the strength of a magnetic field component in the plane of the magnetoresistive elements. In order to monitor the changes in the resistance of the material, associated components such as amplifiers are generally connected together to form an electrical circuit which provides an output signal that is representative of the strength of the magnetic field in the plane of the sensing elements. When the circuit is provided on a silicon substrate, electrical connections between associated components can be made above the surface of the silicon or by appropriately doped regions beneath the components and within the body of the silicon substrate. Components can be connected to each other above the surface of the silicon by disposing conductive material to form electrically conductive paths between the components. When components are connected in electrical communication with each other by appropriately doped regions within the silicon substrate, an electrically conductive path can be formed by diffusing a region of the silicon with an appropriate impurity, such as phosphorous, arsenic or Boron to form electrically conductive connections between the components.
In methods known to those skilled in the art, several problems exist with these types of connections. It is difficult to make both top and bottom electrical connections to an anisotropic magnetoresistive film, such as nickel iron. The selectivity of dry etches and the aggressive nature of wet etches make the process difficult to control.
U.S. Pat. No. 5,005,064, which issued to Yoshino et al on Apr. 2, 1991, discloses a device for detecting magnetism. The device comprises a substrate, an interposed insulating layer containing impurities therein formed on the substrate and a ferromagnetic magnetoresistive element formed on the interposed layer wherein at least a portion of the interposed layer on which the ferromagnetic magnetoresistive element is formed has a concentration of impurities of less than the predetermined value. Furthermore, the surface of the layer interposed between the substrate and the ferromagnetic magnetoresistive element has a surface roughness of less than 120 and an angle between a contacting surface of a conductive wiring and the ferromagnetic magnetoresistive element and the surface of the interposed layer is less than 78 degrees. Therefore, a device wherein a deterioration of the quality film of the ferromagnetic magnetoresistive element can be avoided and a reduction of the ratio of the resistance variation of the ferromagnetic magnetoresistive element can be maintained at less than 10% can be obtained. In addition, the device can effectively suppress the generation of noise so that it is highly sensitive to magnetism and has a high signal-to-noise ratio. Furthermore, the breakdown ratio caused by wiring breakages is effectively reduced.
It would be significantly beneficial if a magnetoresistive material could be disposed on a substrate in such a way that connection to the magnetoresistive material could easily be made from both above the magnetoresistive element and from below the magnetoresistive element. It would also be beneficial if the electrical contact did not degrade the magnetoresistive material. The protective sheath should be of significant bulk resistance to have a minimal effect on the sensitivity of the magnetoresistive material. The sheath should be of a very protective nature so as to allow patterning using photoresist and not degrade the magnetoresistive or the electrical properties. In other words, a significant benefit could be realized if interconnections to the magnetoresistive element could be made above the surface of the silicon substrate and above the upper surface of the sensing element and if electrical connection could also be made to the magnetoresistive element by conductive regions diffused into the body of the silicon substrate through a diffusion barrier.